The present invention relates generally to the art of chemical processing and more particularly to a method and device for extracting liquid from and/or drying printed circuit boards and similar items.
The drying apparatus of the present invention has particular utility in the manufacture of printed circuit boards and will be described herein with particular reference to such applications. It will be appreciated, however, that the drying apparatus of the present invention may enjoy very broad applicability and may be useful in drying/removing liquid from many different types of workpieces other than circuit boards or portions thereof.
In the routine manufacture of printed circuit boards it is common practice to subject the circuit boards or portions thereof, to various liquid chemical treatments and/or water rinses. Following such liquid treatments and/or water rinses, it is generally desirable to effectuate thorough and complete drying of the circuit board so as to prevent subsequent defects and/or processing problems which are known to occur when residual liquid is allowed to remain thereon.
For example, one process wherein the inner layer components of multilayer circuit boards are subjected to numerous liquid treatments and rinses is the "Method for Sequential Spray Application of Chemical Solutions used in the Manufacture of Circuit Board Inner Layers" described in U.S. patent application Ser. No. 267,044. Specifically, the method described in application Ser. No. 267,044 involves subjecting circuit board inner layers to sequential application of four (4) chemical treatment solutions with intermittent water rinses. The final solution applied in accordance with the method of application Ser. No. 267,044 is a "post-treatment solution" which comprises a silane coupling agent. (e.g. Durabond.TM. 600 PT, E. I. duPont de Nemours, Co., Wilimington, Del.) The silane molecules of such post-treatment solution are intended to chemically bond to tin atoms plated on the surfaces of the inner layers. Thereafter, epoxy adhesive applied to the surface of the board will chemically bond to other sites on the silane molecules. As such, the silane material, in order to be effective in its "coupling" function, must concomitantly bind to the epoxy and the tin atoms plated upon the inner layer surface. Such concomitant binding of the epoxy and the tin by the silane allows the silane to promote firm adhesion of the epoxy adhesive to the underlying inner layer. Accordingly, it is important that the silane containing post-treatment solution be evenly disposed in a thin, even layer over the surfaces of the circuit board inner layers prior to drying thereon. Uneven or excessive deposits of non-tin bound silane, if allowed to remain upon surfaces of the inner layers, may result in separation, delamination, resultant adhesive failure and/or other problems with the finished multilayer circuit board may result. It is desirable that the liquid silane coupling agent solution be metered or spread to an even film upon the surface of the inner layers, such film being preferably of a thickness within the range of approximately 1/10 to 1 mils. If the desired, evenly distributed film of silane solution is subsequently streaked, smudged, or disrupted prior to solvent evaporation/drying thereof, the result may be just as undesirable as if the liquid silane film had not been metered or distributed in the first place. (i.e. the dried silane coating may be too thick in some areas and not thick enough in others.) Thus, in drying the inner layer, care should be taken to avoid excessive impingement of blown air onto the inner layer surfaces as such may result in streaking, rippling, or other disruption of even a properly distributed and evenly metered liquid silane film.
In addition to the method described in application Ser. No. 267,044, various other circuit board manufacturing processes also require efficient extraction of liquid and/or drying of the circuit board surfaces. Examples of other processes wherein drying is critical include, but are not limited to; chemical etching operations, chemical oxidation operations, pumice scrubbing/surface abrasion operations, etc.
The routine drying of liquid laden circuit boards is sometimes made more difficult by inherent structural attributes of the boards themselves. For example, many circuit boards are provided with numerous small holes, apertures or perforations to facilitate subsequent mounting of electrical components. Particular problems are apt to arise when attempting to dry such foraminous circuit boards because residual liquid tends to accumulate and/or collect within the individual holes, apertures or perforations. As a result, standard drying techniques (e.g. blowing heated air over the surface of the circuit board) may fail to adequately extract and/or evaporate liquid from the individual holes, apertures or perforations. Failure to extract and/or dry all liquid from the apertures may interfere with subsequent steps in the manufacture of the circuit board due to the presence of the liquid itself and/or subsequent gassification of the liquid as may cause blowing or surface defects in coatings, delamination, etc.
In view of the above-described shortcomings of the prior art there exists a compelling need for improved circuit board drying equipment capable of extracting and/or drying liquids disposed on the surfaces of circuit boards--including the interior surfaces of any holes, apertures or perforations formed therein.